Chemically amplified resist, polymer for the chemically amplified resist, monomer for the polymer and method for transferring pattern to chemically amplified resist layer

ABSTRACT

Chemically amplified resist is produced on the basis of vinyl polymer having 3-oxo-4-oxabicyclo[3.2.1]otane-2-yl group expressed by general formula (1)                    
     where each of L 1 , L 2 , L 3 , L 4 , L 5  and L 6  is selected from the group consisting of hydrogen atom and alkyl groups having the carbon number from 1 to 8, and the hydrogen atom and/or the alkyl group at L 5  and L 6  are replaced with alkylene groups having the carbon number from 1 to 10 and bonded to each other for forming a ring so that the resist exhibits high transparency to light equal to or less than 220 nm wavelength, large resistance against dry etching and good adhesion to substrates.

FIELD OF THE INVENTION

This invention relates to compounds used in photoresist and, moreparticularly, to chemically amplified photoresist sensitive tofar-ultraviolet light equal in wavelength to or less than 220nanometers, polymer used for producing the chemically amplified resist,monomer for producing the polymer and a method for transferring apattern to a chemically amplified resist layer.

DESCRIPTION OF THE RELATED ART

Pattern images are sequentially transferred to semiconductor wafers inprocesses for fabricating semiconductor devices, and design rules havebeen renewed in the fabrication process. Now, semiconductor devices aredesigned under sub-micron rules, and requirements for thephotolithography get sever and sever.

Manufacturers require 0.13 micron patterns for 1 giga-bit DRAMs (DynamicRandom Access Memory), and research and development efforts are beingmade for the photolithography used in the ultra large scale integration.193-nanometer wavelength ArF excimer laser lithography is disclosed byDonald C. Hofer et. al. in “193 nm Photoresist R & D: The Risk &Challenge”, Journal of Photopolymer Science and Technology, vol. 9, No.3, pages 387-397, 1996. The ArF excimer laser lithography requires newphoto-resist. The ArF excimer laser system is expensive, and the gaseousmixture used therein is short in-lifetime. In these circumstances, thenew photoresist is expected to be highly sensitive to the ArF excimerlaser light as well as the high resolution from the viewpoint of thecost performance.

The chemically amplified photoresist is attractive. The chemicallyamplified photoresist contains photo-acid generator, which acceleratesthe chemical reaction in the photoresist. A typical example of thechemically amplified photoresist is disclosed in Japanese PatentApplication laid-open No. 2-27660. The prior art chemically amplifiedphotoresist contains triphenylsulfonium hexafluoroarsenate and poly(p-tert-butoxycarbonyloxy-a-methylstyrene). The prior art chemicallyamplified photoresist is presently used in KrF excimer laser lithographyas taught by Hiroshi Itoh and C. Grantwillson, American Chemical SocietySymposium Series, vol. 242, pages 11-23, 1984.

When the chemically amplified photoresist is exposed to the light,proton acid is generated from the photo-acid generator. The proton acidreacts with the copolymer in the heat treatment after the exposure tothe light. The amount of reaction per photon, i.e., photoreactionefficiency is enhanced through the acid-catalyzed reaction. Although thephotoreaction efficiency is less than 1 in the conventional photoresist,the chemically amplified photoresist achieves the photoreactionefficiency greater than 1, and most of new products of photoresistpresently developed are of the type chemically amplified.

The ArF excimer laser is an example of the short-wavelength band equalto or less than 220 nanometers. The photoresist available for thephotolithography in the short-wavelength band is expected to betransparent to the exposure light and large in resistance against dryetching. The prior art products of photoresist, which are responsive tog-line with 438 nanometer wavelength, i-line with 365 nanometerwavelength or KrF excimer laser light with 248 nanometer wavelength,contain copolymer having the structural unit with the aromatic ring suchas novolak resin or poly (p-vinylphenol), and the aromatic ring makesthe copolymer resistive against the dry etching.

Although the copolymer with the aromatic ring is preferable for the KrFexcimer laser light or the long wavelength rays, the copolymer exhibitsstrong light absorption to the light in the short wavelength band equalto or greater than 220 nanometer wavelength. In fact, when the prior artphotoresist based on the copolymer is exposed,to the ArF excimer laserlight, most of the ArF excimer laser light is absorbed in the surfaceportion of the prior art photoresist layer, and hardly reaches thesubstrate. This means that any fine pattern is not obtained from theprior art photoresist layer.

As described hereinbefore, the prior art products of photoresist are notavailable for the ArF excimer laser lithography, and the semiconductormanufacturers desire a new product of photoresist available for the ArFexcimer laser lithography. The structural unit of the photoresist isexpected to exhibit large resistance against dry etching without thearomatic ring, because the photoresist would exhibit the transparency tothe ArF excimer laser light.

The prior art photoresist available for 193 nm ArF excimer laserlithography is taught by Takechi et. al., Journal of PhotopolymerScience and Technology, vol. 5, No. 3, pages 439 to 446, 1992. Thephotoresist is based on copolymer having adamantyl methacrylate unitswhich are alicylic polymer. Another prior art photoresist is based oncopolymer having isobornyl methacrylate units as disclosed by R. D.Allen et. al, Journal of Photopolymer Science and Technology, vol. 8,No. 4, pages 623 to 636, 1995 and vol. 9, No. 3, pages 465-474, 1996.Yet another prior art photoresist is based on copolymer having thestructural unit of alternating copolymerization between norbornene andmaleic anhidride as taught by F. M. Houlihan et. al, Macromolecules,vol. 30, pages 6517-6524, 1997.

Carboxy group and hydroxy group are categorized in the polar groups. Thepolar group makes the photoresist strongly held in contact withsubstrates, and are preferable to the photoresist. However, theaforementioned monomer, which has the alicylic group, does not have anypolar group. The prior art photoresist is hydrophobic, and thephotoresist layer is liable to peel off from the substrates such assilicon substrates. Thus, the first drawback inherent in the prior artphotoresist is the weak adhesion to substrates.

The second drawback inherent in the photoresist containing the polymerhaving an alicylic group is poor uniformity of film formation. When theprior art photoresist is spread over substrates, the prior artphotoresist layers are irregular in thickness. This phenomenon is alsoderived from the hydrophobic property due to the lack of the polargroup.

The third drawback is a small difference in solubility between thepre-exposure to light and the post-exposure. Adamantyl—containingresidue, isobornyl—containing residue and menthyl—containing residuegive the strong resistance against dry etching to the photoresist.However, the prior art photoresist does not have any residue which makesthe photoresist widely different in solubility between the pre-exposureto light and the post-exposure. This means that the photoresist layerhas a dull edge.

It is possible to overcome those drawbacks by employing copolymerizationwith certain comonomers for improving the difference in solubilityand/or comonomers for enhancing the adhesion to substrates. t-butylmethacrylate and tetrahydropyranyl methacrylate are examples of thecomonomer for improving the difference in solubility, and methacrylicacid is an example of the comonomer for enhancing the adhesion tosubstrates. However, the comonomer is required at least 50 mole %. Thecomonomer is less resistive against dry etching. Thus, the manufacturersdesire new photoresist which exhibits high transparency to the exposurelight, large difference in the solubility and strong adhesion tosubstrates without sacrifice of the resistance against dry etching.

The other sorts of photoresist, which contain the alternatingcopolymerization between norbornene and maleic anhydride, have thenorbornane ring. The norbornane ring also does not have any polar group,and the photoresist exhibits poor adhesion. When copolymer with acrylicacid is introduced into the resin based on the alternating copolymerbetween norbornene and maleic anhydride, the adhesion is improved.However, the resultant photoresist is less resistive against dryetching. The manufacturers also desire new photoresist exhibiting strongadhesion to substrates without sacrifice of the resistance against dryetching.

SUMMARY OF THE INVENTION

It is therefore an important object of the present invention to providephotoresist which exhibits high transparency to light equal inwavelength to or less than 220 nm, large resistance against dry etchingand strong adhesion to substrates.

It is another important object of the present invention to providepolymer to be used in the photoresist.

It is yet another important object of the present invention to providemonomer to be used in the polymer.

It is still another important object of the present invention to providea method for transferring a pattern to the photoresist layer.

The present inventors found that 3-oxo-4-oxabicyclo[3.2.1]otane-2-ylskeleton was useful for photoresist. The present inventors examineddocuments referring to photoresist having the skeleton. Japanese PatentApplication laid-open No. 2001-188351 taught the photoresist having thebridged alicylic skeleton in which at least one ring is lactone ring.Norbornyl monoene, norbornyl diene, tricyclodecamonoene,tricyclodecadiene, tetracyclodecamonoene and tetracyclodecadiene werewritten in the Japanese Patent Application laid-open as the examples.Japanese Patent Application laid-open No. 2000-26446 taught(meth)acrylate polymer having the bridged lactone structure. However,the present inventors could not find any document teaching that3-oxo-4-oxabicyclo[3.2.1]otane-2-yl skeleton was useful for phoioresist.

In accordance with one aspect of the present invention, there isprovided monomer for a chemically amplified photoresist comprising vinylmonomer having 3-oxo-4-oxabicyclo[3.2.1]otane-2-yl group expressed bygeneral formula (1)

where each of L¹, L², L³, L⁴, L⁵ and L⁶ is selected from the groupconsisting of hydrogen atom and alkyl groups having the carbon numberfrom 1 to 8.

The hydrogen atom or alkyl group at L⁵ and the hydrogen atom or alkylgroup at L⁶ may be replaced with alkylene groups having the carbonnumber 1 to 10 and bonded to each other for forming a ring.

The 3-oxo-4-oxabicyclo[3.2.1]otane-2-yl group expressed by generalformula (1) may be replaced with vinyl monomer with a bridged alicylic δlactone structure expressed by general formula (2)

where each of R² and R³ is selected from the group consisting ofhydrogen and alkyl groups having the carbon number from 1 to 4, each ofR⁴ to R⁶ is selected from the group consisting of hydrogen atom andmethyl group, R⁷ and R⁸ are hydrogen atoms or alkylene groups eachhaving the carbon number from 1 to 10 and bonded for forming a ring andn is zero or 1.

In accordance with another aspect of the present invention, there isprovided polymer used for a chemically amplified photoresist comprisingvinyl polymer having 3-oxo-4-oxabicyclo[3.2.1]otane-²-yl group expressedby general formula (1)

where each of L¹, L², L³, L⁴, L⁵ and L⁶ is selected from the groupconsisting of hydrogen atom and alkyl groups having the carbon numberfrom 1 to 8.

The hydrogen atom or alkyl group at L⁵ and the hydrogen atom or alkylgroup at L⁶ may be replaced with alkylene groups having the carbonnumber 1 to 10 and bonded to each other for forming a ring.

The 3-oxo-4-oxabicyclo[3.2.1]otane-2-yl group expressed by generalformula (1) may be replaced with vinyl monomer with a bridged alicylic δlactone structure expressed by general formula (2)

where each of R² and R³ is selected from the group consisting ofhydrogen and alkyl groups having the carbon number from 1 to 4, each ofR⁴ to R⁶ is selected from the group consisting of hydrogen atom andmethyl group, R⁷ and R⁸ are hydrogen atoms or alkylene groups eachhaving the carbon number from 1 to 10 and bonded for forming a ring andn is zero or 1.

In accordance with yet another aspect of the present invention, there isprovided photoresist comprising polymer including vinyl polymer having3-oxo-4-oxabicyclo[3.2.1]otane-2-yl group expressed by general formula(1)

where each of L¹, L², L³, L⁴, L⁵ and L⁶ is selected from the groupconsisting of hydrogen atom and alkyl groups having the carbon numberfrom 1 to 8, and photo-acid generator generating acid in the presence oflight equal in wavelength to or less than 220 nanometers; the ratio ofthe photo-acid generator to the photoresist is fallen within the rangefrom 0.2% by mass to 30% by mass.

The hydrogen atom or alkyl group at L⁵ and the hydrogen atom or alkylgroup at L⁶ may be replaced with alkylene groups having the carbonnumber 1 to 10 and bonded to each other for forming a ring.

The 3-oxo-4-oxabicyclo[3.2.1]otane-2-yl group expressed by generalformula (1) may be replaced with vinyl monomer with a bridged alicylic δlactone structure expressed by general formula (2)

where each of R² and R³ is selected from the group consisting ofhydrogen and alkyl groups having the carbon number from 1 to 4, each ofR⁴ to R⁶ is selected from the group consisting of hydrogen atom andmethyl group, R⁷ and R⁸ are hydrogen atoms or alkylene groups eachhaving the carbon number from 1 to 10 and bonded for forming a ring andn is zero or 1.

In accordance with still another aspect of the present invention, thereis provided a method for transferring a pattern to a photoresist layer,comprising the steps of a) preparing a substrate and photoresistcomprising polymer including polymer having3-oxo-4-oxabicyclo[3.2.1]otane-2-yl group expressed by general formula(1)

where each of L¹, L², L³, L⁴, L⁵ and L⁶ is selected from the groupconsisting of hydrogen atom and alkyl groups having the carbon numberfrom 1 to 8 and photo-acid generator generating acid in the presence oflight equal in wavelength to or less than 220 nanometers, the ratio ofthe photo-acid generator to the photoresist being fallen within therange from 0.2% by mass to 30% by mass, b) spreading the photoresist onthe substrate for forming a photoresist layer, c) exposing thephotoresist layer to image-carrying light having a wavelength between180 nanometers and 220 nanometers for forming a latent image in thephotoresist layer, and d) developing the latent image so as to patternthe photoresist layer into a photoresist patterned layer.

The hydrogen atom or alkyl group at L⁵ and the hydrogen atom or alkylgroup at L⁶ may be replaced with alkylene groups having the carbonnumber 1 to 10 and bonded to each other for forming a ring.

The 3-oxo-4-oxabicyclo[3.2.1]otane-2-yl group expressed by generalformula (1) may be replaced with vinyl monomer with a bridged alicylic δlactone structure expressed by general formula (2)

where each of R² and R³ is selected from the group consisting ofhydrogen and alkyl groups having the carbon number from 1 to 4, each ofR⁴ to R⁶ is selected from the group consisting of hydrogen atom andmethyl group, R⁷ and R⁸ are hydrogen atoms or alkylene groups eachhaving the carbon number from 1 to 10 and bonded for forming a ring andn is zero or 1

The present inventors selected the 3-oxo-4-oxabicyclo[3.2.1]otane-2-ylskeleton from the bridged alicylic δ lactone skeletons for the polymerused for chemically amplified photoresist according to the presentinvention. The 3-oxo-4-oxabicyclo[3.2.1]otane-2-yl skeleton enhanced thetransparency of the chemically amplified photoresist to the light equalin wavelength to or less than 220 nanometers without sacrifice of theresistance against etching and adhesion to substrates. The reasons forthe preferable features were as follows.

First, the present inventors discovered that bicyclo[3.2.1]otaneskeleton made the photoresist transparent to the light equal inwavelength to or less than 220 nanometers and resistive to dry etching.The reason for the high transparency was that the bridged alicylicstructure did not have any aromatic ring. The carbon density was so highthat the bridged alicylic structure well withstood the dry etching.Especially, the bicyclo[3.2.1]otane had the molecular structuredesirable from the viewpoint of the transparency and the resistanceagainst dry etching. The 3-oxo-4-oxabicyclo[3.2.1]otane-2-yl skeletonincluded the bicyclo[3.2.1.]otane skeleton so that the photoresistaccording to the present invention exhibited high transparency withoutsacrifice of the resistance against the dry etching.

Second, δ lactone ring had the dielectric constant larger in value thanthat of the ester structure, ether structure and alcohol structure.Referring to “CHEMICAL HANDBOOK basic II”, revised edition 3, pages 502to 504, edited by Japanese Chemical Society and published by MaruzenCorporation, the dielectric constant of the compounds having the carbonnumber 4 were as follows. The dielectric constant of γ-buthyrolactonewas 39, the dielectric constant of ethyl accetate was 6.02, thedielectric constant of diethyl ether was 4.535, and the dielectricconstant of 1-butanol was 17.51. Thus, the lactone structure was largerin dielectric constant than the other structures. The large dielectricconstant resulted in clear polarity. Especially, the δ lactone exhibitedan appropriate value of the dielectric constant. The large dieelctricconstant was desirable for adhesion to substrates. The3-oxo-4-oxabicyclo[3.2.1]otane-2-yl skeleton had the δ lactone ring sothat the photoresist according to the present invention achieved strongadhesion to substrates.

The 3-oxo-4-oxabicyclo[3.2.1]otane-2-yl skeleton had both of thebicyclo[3.2.1]otane skeleton and the δ lactone skeleton. This meant thatthe 3-oxo-4-oxabicyclo[3.2.1]otane-2-yl skeleton was expected to exhibitsynergism of the bicyclo[3.2.1]otane skeleton and the δ lactoneskeleton. Thus, the 3-oxo-4-oxabicyclo[3.2.1]otane-2-yl skeleton wasdesirable for the transparency to the light, resistance against dryetching and strong adhesion to substrates.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Monomer and Polymer

Any vinyl monomer is available for the chemically amplified photoresistaccording to the present invention in so far as the vinyl monomer isactive in polymerization. From this viewpoint, it is preferable to useethylene, a derivative of ethylene, vinyl chloride, a derivative ofvinyl chloride, styrene, a derivative of styrene, acrylonitrile, aderivative of acrylonitrile, (meth)acrylate, a derivative of(meth)acrylate, norbornene carboxylic acid ester or a derivative ofnorbornene carboxylic acid ester for polymer. When the polymer isproduced from the ethylene, a derivative of ethylene, vinyl chloride, aderivative of vinyl chloride, styrene, a derivative of styrene,acrylonitrile, a derivative of acrylonitrile, (meth)acrylate, aderivative of (meth)acrylate, norbornene carboxylic acid ester or aderivative of norbornene carboxylic acid ester, the vinyl polymer hasrepeated structural unit produced through the vinyl polymerization inthe principal chain.

More particularly, it is preferable to use the derivatives of(meth)acrylate having the bridged alicylic δ lactone structure expressedby general formula (3) as the structural unit

where R¹ is selected from the group consisting of hydrogen atom andmethyl group, each of R² and R³ is selected from the group consisting ofhydrogen atom and alkyl groups having the carbon numbers from 1 to 4,each of R⁴, R⁵ and R⁶ is selected from the group consisting of hydrogenatom and methyl group, R⁷ and R⁸ are hydrogen atoms or alkylene groupshaving the carbon number from 1 to 10 and bonded to each other forforming a ring and n is zero or 1.

When the derivative of (meth)acrylate is vinyl polymerized, theresultant polymer in the acrylic series has the bridged alicylic δlactone structure expressed by general formula (3′) in the principalchain as the repeated structural unit.

where R¹ is selected from the group consisting of hydrogen atom andmethyl group, each of R² and R³ is selected from the group consisting ofhydrogen atom and alkyl groups having the carbon numbers from 1 to 4,each of R⁴, R⁵ and R⁶ is selected from the group consisting of hydrogenatom and methyl group, R⁷ and R⁸ are hydrogen atoms or alkylene groupshaving the carbon number from 1 to 10 and bonded to each other forforming a ring and n is zero or 1.

The derivatives of (meth)acrylate may have alicylic lactone structureexpressed by general formula (3″)

where R¹, R⁴, R⁵ and R⁶ are hydrogen atoms or methyl groups, R² and R³are hydrogen atoms or alkyl groups having the carbon number from 1 to 4and R⁷ and R⁸ are hydrogen atoms or alkylene groups bonded to each otherfor forming a ring. When the derivative of (meth)acrylate having thestructural unit expressed by general formula (3″) is polymerized, theresultant polymer has the structural unit expressed by general formula(3′″) in the principal chain.

where R¹, R⁴, R⁵ and R⁶ are hydrogen atoms or methyl groups, R² and R³are hydrogen atoms or alkyl groups having the carbon number from 1 to 4and R⁷ and R⁸ are hydrogen atoms or alkylene groups bonded to each otherfor forming a ring. When chemically amplified resist is produced on thebasis of the polymer having the structural unit expressed by the generalformula (3′″), the chemically amplified resist contains photo-acidgenerator. It is preferable that the polymer ranges from 70% to 99.8% bymass in the total mass of the polymer and the photo-acid generator.

Derivatives of norbornene carboxylic acid ester are also preferable. Thederivatives of norbornene carboxylic acid ester have a bridged alicylicδ lactone structure expressed by general formula (4)

where R¹ is selected from the group consisting of hydrogen atom andmethyl group, each of R² and R³ is selected from the group consisting ofhydrogen atom and alkyl groups having the carbon number from 1 to 4,each of R⁴, R⁵ and R⁶ is selected from the group consisting of hydrogenatom and methyl group, R⁷ and R⁸ are hydrogen atoms or alkylene groupshaving the carbon number from 1 to 10 and bonded to each other forforming a ring and n is zero or 1.

When the derivative of norbornene carboxylic acid ester with the bridgedalicylic δ lactone structure expressed by general formula (4) ispolymerized, the resultant polymer has a bridged alicylic δ lactonestructure expressed by general formula (4′) in the principal chain asthe repeated structural unit

where R¹ is selected from the group consisting of hydrogen atom andmethyl group, each of R² and R³ is selected from the group consisting ofhydrogen atom and alkyl groups having the carbon number from 1 to 4,each of R⁴, R⁵ and R⁶ is selected from the group consisting of hydrogenatom and methyl group, R⁷ and R⁸ are hydrogen atoms or alkylene groupshaving the carbon number from 1 to 10 and bonded to each other forforming a ring and n is zero or 1.

More than one vinyl monomer may be copolymerized. When more than onevinyl monomer is copolymerized, the resultant copolymer has more thanone structural unit in the principal chain as the repeated structuralunit. Thus, a wide variety of desirable properties are given to thephotoresist according to the present invention by using the copolymers.

As described hereinbefore, each of the R¹, R⁴, R⁵ and R⁶is a hydrogenatom or methyl group in the general formulae (2), (3), (4), (3′) and(4′). In those general formulae, each of the R² and R³ is a hydrogenatom or alkyl group having the carbon number from 1 to 4, i.e., methylgroup, ethyl group, n-propyl group and n-butyl. R⁷ and R⁸ are hydrogenatoms or alkylene groups, which have the carbon number from 1 to 10 andare bonded to each other for forming a ring. Examples are propylenegroup [—(CH₂)₃—], butylene group [—(CH₂)₄—] and 1,3-cyclopentylenegroup.

In the general formula (1), L¹ is exchangeable for R⁴, L² isexchangeable for R⁵, L³ and L⁴ are independently exchangeable for R⁶, L⁵is exchangeable for R⁷, and L⁶ is exchangeable for R⁸.

For examples, in case where the derivatives of (meth)acrylate have nequal to 1, following compounds are available for the polymer and,accordingly, photoresist.

In case where the derivatives of norbornene carboxylic acid ester have nequal to 1, following compounds are available for the polymer and,accordingly, the photoresist.

In case where the derivatives of (meth)acrylate have n equal to zero,following compounds are available for the polymer and photoresist.

In case where the derivatives of norbornene carboxylic acid ester have nequal to zero, followings are available for the polymer and thephotoresist.

In addition to the above-described repeated structural unit, comonomermay be copolymerized so as to introduce a repeated structural unit to bedecomposed by acid produced from photo-acid generator and/or anotherrepeated structural unit expected to impart various desirable featuresinto the polymer.

The repeated structural units, which are produced from the comonomer,are expected to exhibit a high decomposition efficiency, impartdesirable features to the polymer and have good affinity to the vinylpolymerization. From these viewpoints, it is desirable to have at leastone of the structural units expressed by the general formulae (3′a),(3′b) and (3′c).

where R⁹ is selected from the group consisting of hydrogen atom andmethyl group, R¹⁰ is selected from the group consisting of groups to bedecomposed by acid and bridged cyclic hydrocarbon groups having thecarbon number from 7 to 13 and having groups to be decomposed by acid,R¹¹ is selected from the group consisting of hydrogen atom and methylgroup, R¹² is selected from the group consisting of hydrogen atom,hydrocarbon groups having the carbon number from 1 to 12, bridged cyclichydrocarbon groups having the carbon number from 7 to 13 and eitherhydroxy or carboxy group and 2,6-norbornanecarbolactone-5-yl group and Mis selected from the group consisting of hydrogen atom, hydroxy group,hydroxyalkyl groups and acid dissociated organic groups having thecarbon number equal to or less than 20 and to be decomposed by acid forproducing carboxy group.

R¹⁰ is the group to be decomposed by acid or the bridged cyclichydrocarbon groups, which have the carbon number from 7 to 13 and agroup to be decomposed by acid. Examples of the group to be decomposedby acid are t-butyl, tetrahydropyran-2-yl group, tetrahydrofuran-2-ylgroup, 4-methoxytetrahydropyran-4-yl group, 1-ethoxyethyl group,1-butoxyethyl group, 1-propoxyethyl group, 3-oxocyclohexyl group,2-methyl-2-adamantyl group, 2-ethyl-2-adamantyl group,1-methyl-1-adamantylethyl group, 8-methyl-8-tricyclo[5.2.1.0^(2,6)]decylgroup, 1,2,7,7-tetramethyl-2-norbornyl group, 2-acetoxymentyl group,2-hydroxymentyl group and 1-methyl-1-cyclohexylethyl group.

Examples of the bridged cyclic hydrocarbon groups having the carbonnumber from 7 to 13 and a group to be decomposed by acid have estergroup, and are tricyclo[5.2.1.0^(2,6)]decyl methyl group,tricyclo[5.2.1.0^(2,6)]decyl group, adamantyl group, norbornyl group,methylnorbornyl group, isobornyl group,tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecyl group andmethyltetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecyl group. The chemicalstructures of these groups are as follows.

tricyclo[5.2.1.0^(2,6)]decyl methyl group

or with ester group,

tricyclo[5.2.1.0^(2,6)]decyl group

or with ester group,

adamantyl group,

with ester group,

norbornyl group

with ester group,

methylnorbornyl group

with ester group,

isobornyl group

with ester group,

tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecyl group

with ester group,

methyltetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecyl group

with ester group,

In the chemical structures, R¹⁷ is the group to be decomposed by acid,and examples of the group are t-butyl, tetrahydropyran-2-yl group,tetrahydrofuran-2-yl group, 4-methoxytetrahydropyran-4-yl group,1-ethoxyethyl group, 1-butoxyethyl group, 1-propoxyethyl group,3-oxocyclohexyl group, 2-methyl-2-adamantyl group, 2-ethyl-2-admantylgroup, 8-methyl-8-tricyclo[5.2.1.0^(2,6)]decyl group,1,2,7,7-tetramethyl-2-norbornyl group, 2-acetoxymenthyl group,2-hydroxymenthyl group and 1-methyl-1-cyclohexylethyl group.

In case where R¹² is a hydrocarbon group having the carbon number from 1to 12, examples of R¹² are methyl group, ethyl group, n-propyl group,isopropyl group, n-butyl group, isobutyl group, t-butyl group,cyclohexyl group, tricyclo[5.2.1.0^(2,6)]decyl group, adamantyl group,norbornyl group, isobornyl group andtetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecyl group.

Examples of the bridged cyclic hydrocarbon having the carbon number from7 to 13 and one of the hydroxy group and carboxy group arehydroxyadamantyl group, dihydroxyadamantyl group, hydroxynorbornylgroup, hydroxytetracyclododecyl group, carboxyadamantyl group,carboxynorbornyl group and carboxytetracyclododecyl group.

In case where M is hydroxyalkyl group, examples of M are hydroxymethylgroup and hydroxyethyl group.

In case where M is the acid dissociated organic group having the carbonnumber equal to or less than 20 and to be decomposed by acid forproducing carboxy group, examples of M are t-butoxycarbonyl group,tetrahydropy-ranyloxycarbonyl group, tetrahydrofuranyloxycarbonyl group,4-methoxy tetorahydropyranyloxycarbonyl group, 1-ethoxyethoxycarbonylgroup, 1-butoxyethoxycarbonyl group, 1-propoxyethoxycarbonyl group,3-oxocyclohexyloxycarbonyl group, 2-methyl-2-admantyloxycarbonyl group,2-ethyl-2-adamantyloxycarbonyl group,8-methyl-8-tricyclo[5.2.1.0^(2,6)]decyloxycarbonyl group,1,2,7,7-tetramethyl-2-norbornyloxycarbonyl group,2-acetoxymenthyloxycarbonyl group, 2-hydroxymenthyloxycarbonyl group and1-methyl-1-cyclohexylethoxycarbonyl group.

Other repeated structural units are expected to enhance thedecomposition efficiency and/or give the photoresist other desirablefeatures. Comonomers for these repeated structural units are to be wellpolymerized for producing vinyl polymer. From this viewpoint, at leastone of the structural units expressed by the general formulae (4′a),(4′b) and (4′c) is preferable.

where R¹³ is selected from the group consisting of hydrogen atom andmethyl group, R¹⁴ is selected from the group consisting of hydroxygroup, hydroxyalkyl group and acid dissociated organic groups having thecarbon number equal to or less than 20 and to be decomposed by acid forproducing carboxy group, R¹⁶ is selected from the group consisting ofhydrogen atom and methyl group and R¹⁶ is selected from the groupconsisting of hydroxy group, hydroxyalkyl group and acid dissociatedorganic groups having the carbon number equal to or less than 20 and tobe decomposed by acid for producing carboxy group.

Each of R¹⁴ and R¹⁶ is hydroxy group, hydroxyalkyl group such ashydroxymethyl group and hydroxyethyl group or acid dissociated organicgroups having the carbon number equal to or less than 20 and to bedecomposed by acid for producing carboxy group. The group of aciddissociated organic groups contains t-butoxycarbonyl group,tetrahydropyranyloxycarbonyl group, tetrahydrofuranyloxycarbonyl group,4-methoxytetrahydropyranyloxycarbonyl group, 1-ethoxyethoxycarbonylgroup, 1-butoxyethoxycarbonyl group, 1-propoxyethoxycarbonyl group,3-oxocyclohyxyloxycarbonyl group, 2-methyl-2-adamantyloxycarbonyl group,2-ethyl-2-adamantyloxycarbonyl group,8-methyl-8-tricyclo[5.2.1.0^(2,6)]decyloxycarbonyl group,1,2,7,7-tetramethyl-2-norbornyloxycarbonyl group,2-acetoxymenthyloxycarbonyl group, 2-hydroxymenthyloxycarbonyl group and1-methyl-1-cyclohexylethoxycarbonyl group.

From the viewpoint of desirable properties of resultant copolymer, it ispreferable to copolymerize each of the repeated structural unitsexpressed by the general formulae (3′a), (3′b) and (3′c) with at leastone of the repeated structural unit expressed by the general formulae(4′a), (4′b) and (4′c). It is also preferable to copolymerize each ofthe repeated structural units expressed by the general formulae (4′a),(4′b) and (4′c) with at least one of the repeated structural unitexpressed by the general formulae (3′a), (3′b) and (3′c). The repeatedstructural units expressed by the general formulae (3′a) to (3′c) may beselectively incorporated in the polymer concurrently with the repeatedstructural units expressed by the general formulae (4′a) to (4′c) so asto give a wide variety of desirable properties to the polymer.

It is preferable that the copolymer contains at least one of therepeated structural units expressed by the general formulae (3′) and(4′) fallen within the range between 5 mole % and 90 mole % from theviewpoint of the properties of the resultant polymer. It is morepreferable that at least one of the repeated structural units expressedby the general formulae (3′) and (4′) is fallen within the range between7 mole % and 80 mole %. It is much more preferable that at least one ofthe repeated structural units expressed by the general formulae (3′) and(4′) is fallen within the range between 10 mole % and 70 mole %.

Since the repeated structural units expressed by the general formulae(3′a) to (3′c) well react with the derivatives of (meth)acrylateexpressed by the general formula (3), it is preferable to make therepeated structural unit or units expressed by the general formulae(3′a) to (3′c) copolymerized with the repeated structural unit expressedby the general formula (3′). In this instance, it is preferable that thestructural unit expressed by general formula (3′) is fallen within therange between 5 mole % and 90 mole % of the copolymer. It is morepreferable that the structural unit expressed by general formula (3′) isfallen within the range between 7 mole % and 80 mole % of the copolymer.It is much more preferable that the structural unit expressed by generalformula (3′) is fallen within the range between 10 mole % and 70 mole %of the copolymer.

Since the repeated structural units expressed by the general formulae(4′a) to (4′c) well react with the derivatives of norbornene carboxylicacid ester expressed by the general formula (4), it is preferable tomake the repeated structural unit or units expressed by the generalformulae (4′a) to (4′c) copolymerized with the repeated structural unitexpressed by the general formula (4′). In this instance, it ispreferable that the structural unit expressed by general formula (4′) isfallen within the range between 5 mole % and 90 mole % of the copolymer.It is more preferable that the structural unit expressed by generalformula (4′) is fallen within the range between 7 mole % and 80 mole %of the copolymer. It is much more preferable that the structural unitexpressed by general formula (4′) is fallen within the range between 10mole % and 70 mole % of the copolymer.

The polymers described hereinbefore are produced through a usualpolymerization process such as, for example, the radical polymerization,anionic polymerization or addition polymerization. A suitablepolymerization initiator such as, for example, azobisisobutyronitrile(AIBN) is, by way of example, added to dry tetrahydrofuran in inertatmosphere such as argon or nitrogen, and the polymerization initiatorand the dry tetrahydrofuran are agitated at 50 degrees to 70 degrees incentigrade for 0.5 hour to 12 hours. Then, the polymer is producedthrough the radical polymerization.

In case where the polymer is produced through the additionpolymerization, the polymer may be produced through the processdisclosed by J. P. Mathew, Macromolecules, vol. 29, pages 2755 to 2763,1996. Namely, suitable catalyst in palladium compound series is used inthe addition polymerization. (η³-allyl) Pd(BF₄), (η³-allyl) Pd (SbF₆)and [Pd (CH₃CN)₄] (BF₄)₂ are examples of the palladium compoundcatalyst. Otherwise, nickel compound catalyst such as bis(pentafluorophenyl) nickel toluene complex is used in the additionpolymerization as taught by T. Chiba et. al, Journal of PhotopolymerScience and Technology, vol. 13, No. 4, pages 657 to 664, 2000.

The weight average molecular weight of the polymer available for thephotoresist according to the present invention is fallen within therange from 2,000 to 200,000.

Chemically Amplified Resist

Chemically amplified resist embodying the present invention contains atleast the polymer described hereinbefore and photo-acid generator. Incase where n and both of R² and R³ are 1 and alkyl group in thestructural unit expressed by the general formula (3′), the alicyliclactone unit is a tertiary ester of carboxylic acid, and is eliminatedin the presence of acid. Thus, it is an acid decomposed group. Thereaction is as follows.

It is preferable that the photo-acid generator generates acid in thepresence of the light equal in wavelength to or less than 400nanometers. It is more preferable to produce the acid in the presence ofthe light having the wavelength between 180 nanometers and 220nanometers. There is not any limit to the photo-acid generator in so faras liquid mixture, in which the mixture containing the photo-acidgenerator and the polymer such as the polymer in acrylic series is welldissolved in organic solvent, is uniformly spread by using a spincoater, by way of example. More than one photo-acid generator may bemixed with the polymer.

Examples of the photo-acid generator are derivatives oftriphenylsulfonium salt, derivatives of diphenyliodonium salt,derivatives of dialkylphenacylsulfonium salt, derivatives ofnitrobenzylsulfonate and derivatives of sulfonic acid ester ofN-hydroxysuccinimide.

Another photo-acid generator is disclosed by J. V. Crivello et. al,Journal of the Organic Chemistry, vol. 43, No. 15, pages 3055 to 3058,1978. J. V. Crivello et. al. teach derivatives of triphenylsulfoniumsalt and other onium salts such as sulfonium salt, iodonium salt,phosphonium salt, diazonium salt and ammonium salt. Yet anotherphoto-acid generator is disclosed by O. Nalamasu et. al, SPIEProceedings, vol. 1262, page 32, 1990. O. Nalamasu et. al. teach2,6-dinitrobenzyl esters. Still another photo-acid generator isdisclosed by Takumi Ueno et. al, Proceedings of PME′89, Kohdansha, pages413 to 424, 1990, and Ueno et. al. teach1,2,3-tri(methanesulfonyloxy)benzen. Yet another photo-acid generator isdisclosed in Japanese Patent Application laid-open No. 5-134416, and issulfosuccinimide.

From the viewpoint that the photo-acid generator makes the chemicallyamplified resist well sensitive to the exposure light for producing afine latent image therein, it is preferable that the content of thephoto-acid generator is equal to or greater than 0.2% by mass of bothpolymer and photo-acid generator. It is more preferable that thechemically amplified resist contains the photo-acid generator equal toor greater than 1% by mass of both polymer and photo-acid generator.However, if the content of photo-acid generator is greater than 30% bymass, the chemically amplified resist is less liable to be uniformlyspread, and the scum is not ignorable after the development. Thus, theupper limit of the content is 30% by mass. It is more preferable thatthe content of the photo-acid generator is equal to or less than 15% bymass. Thus, the photo-acid generator is to range from 0.2% by mass to30% by mass, and the more preferable range is between 1% by mass and 15%by mass.

When the manufacturer prepares the chemically amplified resist,appropriate solvent is used. Any organic solvent is available for thechemically amplified resist in so far as the polymer and the photo-acidgenerator are well dissolved therein for being uniformly spread oversubstrates. Only one sort of solvent or more than one sort of solvent isused for preparing the chemically amplified resist according to thepresent invention.

Examples of the solvent are n-propyl alcohol, iso-propyl alcohol,n-butyl alcohol, tert-butyl alcohol, propylene glycol monomethyletheracetate, propylene glycol monoethylether acetate, methyl cellosolveacetate, ethyl cellosolve acetate, ethyl lactate, methyl lactate,2-methoxybutyl acetate, 2-ethoxyethyl acetate, methyl, pyruvate, ethylpyruvate, 3-methoxy methyl propionate, 3-methoxy ethyl propionate,N-methyl-2-pyrrolidinone, cyclohexanone, cyclopentanone, cyclohexanol,methyl ethyl ketone, 1,4-dioxane, ethyleneglycolmonomethylether,ethyleneglycolmonomethylether acetate, ethyleneglycolmonoethylether,ethyleneglycolmonoisopropylether, diethyleneglycolmonomethylether anddiethyleneglicoldimethylether.

The chemically amplified resist according to the present invention mayfurther contain other additives such as, for example, dissolutioninhibitor, organic base, surface active agent, dyestuff, stabilizer,coating property improving agent and coloring agent.

Pattern Transfer

A pattern image is transferred from a photo-mask to a chemicallyamplified resist layer as follows. First, the chemically amplifiedresist described hereinbefore is prepared. The chemically amplifiedresist solution is spread over a layer such as, for example, asemiconductor wafer or a semiconductor/insulating layer on thesemiconductor wafer. A spin coater may be used for spreading thechemically amplified resist solution.

Subsequently, the chemically amplified resist layer is pre-baked, and,thereafter, the semiconductor wafer is inserted into a chamber of analigner. The aligner is well known to skilled person, and no furtherdescription is hereinbelow incorporated. Laser light is radiated from alight source to a photo-mask. The laser light has the wavelength between180 nanometers and 220 nanometers. In this instance, the light sourceradiates 193 nanometer wavelength ArF excimer laser light. The ArFexcimer laser light passes through the photo-mask, and carries thepattern image on the photo-mask. The image-carrying light reaches thechemically amplified resist layer. The image-carrying light produces alatent image in the chemically amplified resist layer.

The semiconductor wafer is taken out from the aligner, and the latentimage is developed. Then, the chemically amplified resist layer ispatterned into a resist mask. Using the resist mask, thesemiconductor/insulating layer is, by way of example, selectivelyetched. Otherwise, dopant impurity may be ion implanted into thesemiconductor/insulting layer or semiconductor wafer. Thus, thesemiconductor device manufactures form miniature patterns on or over thesemiconductor wafers.

Description is hereinbelow made on several examples. However, theseexamples do not set any limit to the scope of the present invention.Highpurity reagents and other chemicals used in the examples werepurchased in the market. However, when special reagent or chemical wasused, the special reagent/chemical is detailed.

FIRST EXAMPLE

The present inventors synthesized methacrylate, i.e., Methacrylate 1through the following reaction formula.

The methacrylate, i.e., Methacrylate 1 was expressed by the generalformula (3) where R¹, R² and R³ were methyl groups, R⁴, R⁵ and R⁶ werehydrogen atoms, R⁷ and R⁸ were propylene groups, i.e., [—(CH₂)₃—] bondedto each other for forming a ring and n was 1.

In detail, 25.4 grams of tricyclodecane-8-one was dissolved in 150milliliters of methylene chloride, and 42.6 grams of sodium hydrogencarbonate was added to the resultant solution. 50 grams ofm-chloroperbenzoic acid dissolved in 400 milliliters of methylenechloride was further dropped into the resultant solution. The resultantsolution was agitated all night at room temperature. Then, sodiumm-chlorobenzoate acid was deposited, and was filtrated. The filtrate waswashed in 5% water solution of sodium sulfite, thereafter, in 5% watersolution of sodium carbonate and, finally, in brine. The organic layerwas dried with MgSO₄, and methylene chloride was eliminated in vacuumtherefrom. The residue was distilled in vacuum, i.e., 0.35 mm Hg at 1 10degrees to 111 degrees in centigrade. Then, 24.8 grams of lactone 1 wasobtained. The yield was 88%.

Subsequently, 140 milliliters of dry THF was cooled to −78 degrees incentigrade, and 70 milliliters of 2 mole/1 THF solution of lithiumdiisopropyl amide was dropped thereinto in argon atmosphere. 10 grams ofthe lactone compound, i.e., Lactone 1, was dissolved in 20 millilitersof dry THF, and the resultant solution was further dropped thereinto.Reaction proceeded for an hour at −78 degrees in centigrade, and 26.6grams of acetone was dropped thereinto. The resultant solution wasagitated for 4 hours, and 10% hydrochloric acid water solution was addedto the resultant solution until the solution was changed to acid. Anorganic layer was extracted from the solution by using 300 millilitersof ethyl acetate. The organic layer was washed in 5% of sodium hydrogencarbonate and, thereafter, in brine. After the washing, the organiclayer was dried with magnesium sulfate, and the solvent was eliminatedin vacuum. Hexane was added to the residue, and, thereafter, cooled.Then, a piece of crystal was precipitated, and was filtered. 6.04 gramsof alcohol compound, i.e., Alcohol 1 was obtained. The yield was 24%.

7 grams of alcohol, 3.79 grams of triethylamine and 9 milligram ofphenothiazine were dissolved in 30 milliliters of dry methylenechloride, and solution, in which 3.26 grams of methacryloyl chloride wasdissolved in 5 milliliters of dry methylane chloride, was dropped intothe resultant solution cooled with ice. The resultant solution wascontinuously cooled with ice for 3 hours, and, thereafter, was agitatedthrough all night at room temperature.

Subsequently, 200 milliliters of ethyl acetate was added, and an organiclayer was obtained. The organic layer was washed in 0.5 N hydrochloricacid, thereafter, in 3% water solution of sodium hydrogen carbonate and,finally, in brine. The organic layer was dried with magnesium sulfate,and the solvent was eliminated in vacuum. The residue was separated andrefined through a silica gel column. Elute contained hexane and ethylacetate at 5:1.2.4 grams of methacrylate, i.e., Methacrylate 1 wasobtained. The yield was 26%.

The methacrylate was analyzed. The result of ¹H-NMR (CDCl₃) was asfollows; δ was 0.84 to 1.0 (1H, m), 1.0 to 1.13 (1H, m), 1.66 (3H, s),1.78 (3H, s), 1.91 (3H, s), 1.27 to 1.41 (1H, m), 1.67 to 1.75 (2H, m),1.94 to 2.13 (3H, m), 2.25 to 2.41 (2H, m), 2.75 (1H, q), 3.06 (1H, s),4.49 (1H, s), 5.54 (1H, s) and 6.04 (1H, s).

The result of 1R (KBr) was as follows; 2850, 2950 (υC—H), 1712, 1728(υC═O), 1632 (υC═C) and 1136, 1184 (υC−O)cm⁻¹.

SECOND EXAMPLE

The present inventors synthesized acrylate expressed as follows.

The acrylate was expressed by the general formula (3) where where R¹,R⁴, R⁵ and R⁶ were hydrogen atoms, R² and R³ were methyl groups, R⁷ andR⁸ were propylene groups, i.e., [—(CH₂)₃—] bonded to each other forforming a ring and n was 1.

The acrylate was synthesized as similar to the synthesis of themethacrylate except that the methacryloyl chloride was replaced withacryloyl chloride. The yield was 21%.

The acrylate was analyzed. The result of ¹H-NMR (CDCl₃) was as follows;δ was 0.87 to 1.12 (2H, m), 1.24 to 1.42 (1H, m), 1.62 (3H, s), 1.78(3H, s), 1.65 to 1.77 (2H, m), 1.90 to 2.11 (2H, m), 2.26 to 2.41 (3H,m), 2.75 (1H, q), 3.17 (1H, s), 4.48 (1H, s), 5.58 (1H, d), 6.03 (1H,dd) and 6.34 (1H, d).

The result of 1R (KBr) was as follows; 2850, 2950 (υC—H), 1720 (υC═O),1616, 1632 (υC═C) and 1140, 1192 (υC—O) cm⁻¹.

THIRD EXAMPLE

The present inventors further synthesized acrylate, i.e., Acrylate 1through the following reaction formula.

The acrylate, i.e., Acrylate 1 was expressed by the general formula (3)where R¹, R², R³, R⁴, R⁵ and R⁶ were hydrogen atoms, R⁷ and R⁸ werepropylene groups, i.e., [—(CH₂)₃—] bonded to each other for forming aring and n was 1.

The synthesis for the acrylate was similar to that for the first exampleexcept that the acetone was replaced with formaldehyde in the synthesisof the alcohol compound, i.e., Alcohol 2 and that the methacryloylchloride was replaced with acryloyl chloride. The yield was 18%

The acrylate was analyzed. The result of ¹H-NMR (CDCl₃) was as follows;δ was 0.88 to 1.19 (2H, m), 1.28 to 1.43 (1H, m), 1.56 to 1.85 (2H, m),1.93 to 2.11 (3H, m), 2.16 to 2.22 (1H, m), 2.34 to 2.45 (1H, m), 2.69to 2.87 (2H, m), 4.44 (1H, d), 4.46 (1H, d), 4.51 (1H, s), 5.88 (1H, d),6.14 (1H, dd) and 6.44 (1H, d).

The result of IR (KBr) was as follows; 2866, 2954 (υC—H), 1732 (υC═O),1635 (υC═C) and 1189 (υC—O) cm⁻¹.

FOURTH EXAMPLE

The present inventors synthesized polymer, which contained a structuralunit expressed by the general formula (3′) at 50 mole % and anotherstructural unit expressed by the general formula (3′b) at 50 mole %.These structural units were as follows.

The first structural unit was expressed by the general formula (3′)where R¹, R² and R³ were methyl groups, R⁴, R⁵ and R⁶ were hydrogenatoms, R⁷ and R⁸ were propylene groups, i.e., [—(CH₂)₃—] bonded to eachother for forming a ring and n was 1. The second structural unit wasexpressed by the general formula (3′b) where R¹¹ was methyl group andR¹² was 2,6-norbornanecarbolactone-5-yl group.

The synthesis proceeded as follows. 2.4 grams of methacrylate, which wasobtained through the synthesis for the first example, and 1.82 grams of5-methacryloyloxy-2,6-norbornanecarbolactone were dissolved in 22milliliters of dry tetrahydrofuran in a 100 ml flask. 108 milligrams ofAIBN was added thereto, and was agitated in argon atmosphere at 60degrees to 65 degrees in centigrade. After 3 hours, the solution wascooled, and the reactant mixture was poured into 400 milliliters ofmethanol. Deposited precipitate was filtrated. The filtrate was refined,gain. Thus, 2.95 grams of the polymer was obtained. The yield was 70%.

The polymer was analyzed. The copolymerization ratio was 50:50 on thebasis of the integral ratio of ¹H-NMR. From the result of GPC analysis,weight average molecular weight (Mw) was 9600 (polystyrene), and thedegree of dispersion (Mw/Mn) was 1.83.

FIFTH EXAMPLE AND SIXTH EXAMPLE

The fifth and sixth examples were polymerized as similar to the fourthexample except for the ratio of the monomers as shown in the followingtable.

Ratio of Copolymerization Weight Average Monomers Ratio (by mole)Molecular Weight Fifth Example 0.3/0.7 0.31/0.69  8500 Sixth Example0.7/0.3 0.7/0.3 10800

SEVENTH EXAMPLE AND EIGHTH EXAMPLE

The seventh and eighth examples were polymerized as similar to thefourth example except for the amount of AIBN, i.e., concentration. AIBNconcentration, copolymerization ratio and weight average molecularweight were as follows.

AIBN Copolymerization Weight Average Concentration Ratio (by mole)Molecular Weight Seventh Example 0.5 mole % 0.5/0.5 45000 Eighth Example10 mole % 0.49/0.51  4100

NINTH EXAMPLE

The present inventors synthesized polymer in acrylic series. The polymercontained a structural unit expressed by the general formula (3′) at 50mole % and another structural unit expressed by the general formula(3′a) at 50 mole %. These structural units were as follows.

The first structural unit was expressed by the general formula (3′)where R¹, R², R³, R⁴, R⁵ and R⁶ were hydrogen atoms, R⁷ and R⁸ werepropylene groups, i.e., [—(CH₂)₃—] bonded to each other for forming aring and n was 1. The second structural unit was expressed by thegeneral formula (3′a) where R⁹ was hydrogen atom and R¹⁰ wast-butoxycarbonyltetracyclododecyl group.

The synthesis was similar to that for the fourth example except that thepresent inventors used the monomer of the third example andt-buthoxycarbonyl-tetracyclododecyl acrylate instead of the monomer ofthe first example and 5-methacryloyloxy-2,6-norbomanecarbolactone. Theyield was 54%, and the weight average molecular weight Mw was 10800. Thedegree of dispersion Mw/Mn was 1.84.

TENTH EXAMPLE

The present inventors synthesized polymer in acrylic series. The polymercontained a structural unit expressed by the general formula (3′) at 50mole % and another structural unit expressed by the general formula(3′a) at 50 mole %. These structural units were as follows.

The first structural unit was expressed by the general formula (3′)where R¹, R², R³, R⁴, R⁵ and R⁶ were hydrogen atoms, R⁷ and R⁸ werepropylene groups, i.e., [—(CH₂)₃—] bonded to each other for forming aring and n was 1. The second structural unit was expressed by thegeneral formula (3′a) where R⁹ was hydrogen atom and R¹⁰ was2-methyl-2-adamantyl group.

The synthesis was similar to that for the ninth example except that thepresent inventors used 2-methyl-2-adamantyl acrylate instead oft-butoxycarbonyltetracyclododecyl acrylate. The yield was 51%, and theweight average molecular weight Mw was 9100. The degree of dispersionMw/Mn was 1.92.

ELEVENTH EXAMPLE

The present inventors synthesized polymer in acrylic series. The polymercontained a structural unit expressed by the general formula (3′) at 30mole %, another structural unit expressed by the general formula (3′a)at 50 mole % and yet another structural unit expressed by the generalformula (3′b) at 20 mole %. These structural units were as follows.

The first structural unit was expressed by the general formula (3′)where R¹, R², R³, R⁴, R⁵ and R⁶ were hydrogen atoms, R¹ and R⁸ werepropylene groups, i.e., [—(CH₂)₃—] bonded to each other for forming aring and n was 1. The second structural unit was expressed by thegeneral formula (3′a) where R⁹ was hydrogen atom and R¹⁰ wast-butoxycarbonyltetracyclododecyl group. The third structural unit wasexpressed by the general formula (3′b) where R¹¹ was hydrogen atom andR¹² was 2,6-norbornanecarbolactone-5-yl group.

The synthesis was similar to that for the fourth example. In thesynthesis, the monomer of the third example,t-butoxycarbonyltetracyclododecyl acrylate and5-acryloyloxy-2,6-norbornanecarbolactone were used. The yield was 57%,and the weight average molecular weight Mw was 8700. The degree ofdispersion Mw/Mn was 1.76.

TWELFTH EXAMPLE

The present inventors synthesized polymer in acrylic series. The polymercontained a structural unit expressed by the general formula (3′) at 30mole %, another structural unit expressed by the general formula (3′a)at 50 mole % and yet another structural unit expressed by the generalformula (3′b) at 20 mole %. These structural units were as follows.

The first structural unit was expressed by the general formula (3′)where R¹, R², R³, R⁴, R⁵ and R⁶ were hydrogen atoms, R⁷ and R⁸ werepropylene groups, i.e., [—(CH₂)₃—] bonded to each other for forming aring and n was 1. The second structural unit was expressed by thegeneral formula (3′a) where R⁹ was hydrogen atom and R¹⁰ wast-butoxycarbonyltetracyclododecyl group. The third structural unit wasexpressed by the general formula (3′b) where R¹¹ was methyl group andR¹² was 3-hydroxy-1-admantyl group.

The synthesis was similar to that for the fourth example. In thesynthesis, the monomer of the third example,t-butoxycarbonyltetracyclododecyl acrylate and3-hydroxy-1-adamantylmethacrylate were used. The yield was 48%, and theweight average molecular weight Mw was 10500. The degree of dispersionMw/Mn was 2.02.

THIRTEENTH EXAMPLE

The present inventors synthesized polymer in acrylic series. The polymercontained a structural unit expressed by the general formula (3′) at 50mole % and another structural unit expressed by the general formula(3′c) at 50 mole %. These structural units were as follows.

The first structural unit was expressed by the general formula (3′)where R¹, R² and R³ were methyl groups, R⁴, R⁵ and R⁶ were hydrogenatoms, R⁷ and R⁸ were propylene groups, i.e., [—(CH₂)₃—] bonded to eachother for forming a ring and n was 1. The second structural unit wasexpressed by the general formula (3′c) where M was hydrogen atom.

The synthesis was similar to that for the fourth example. In thesynthesis, the monomer of the first example, norbornene and maleicanhidride were used. The yield was 26%, and the weight average molecularweight Mw was 5600. The degree of dispersion Mw/Mn was 2.24.

FOURTEENTH EXAMPLE

The present inventor synthesized a derivative of norbornene expressed asfollows.

The derivative of norbornene was expressed by the general formula (4)where R¹, R², R³, R⁴, R⁵ and R⁶ were hydrogen atoms, R⁷ and R⁸ werepropylene groups, i.e., [—(CH₂)₃—] bonded to each other for forming aring and n was 1.

The derivative was synthesized as follows. 20 grams of the derivative ofacrylate obtained as the third example was dissolved in 20 millilitersof toluene. 7 grams of cyclopentadiene was dropped into the solutioncooled with ice, and was agitated through all night. Dicyclopentadienewas produced as byproduct, and was eliminated in vacuum. Then, 24.9grams of the derivative of norbornene was obtained. The derivative ofnorbornene was viscous liquid, and the yield was 95%.

The derivative of norbornene was analyzed. The result of ¹H-NMR (CDCl₃)was as follows; δ was 0.84 to 1.17 (2H, m), 1.19 to 1.53 (4H, m), 1.65to 2.45 (8H, m), 2.64 to 3.3 (4H, m), 4.16 to 4.4 (2H, m), 4.5 (1H, s),5.8 to 5.98 (1H, m) and 6.1 to 6.3 (1H, m). The result of 1R(KBr) was asfollows; 2951, 2866 (υC—H), 1843, 1721 (υC═O), 1185 (υC—O) cm⁻¹.

FIFTEENTH EXAMPLE

The present inventors further synthesized another derivative ofnorbornene expressed as follows.

The derivative of norbornene was expressed by the general formula (4)where R¹, R⁴, R⁵ and R⁶ were hydrogen atoms, R² and R³ were methylgroups, R⁷ and R⁸ were propylene groups, i.e., [—(CH₂)₃—] bonded to eachother for forming a ring and n was 1.

The derivative of norbornene was synthesized as similar to that of thefourteenth example except that the present inventors used acrylate ofthe second example instead of the acrylate of the third example.

SIXTEENTH EXAMPLE

The present inventors synthesized polymer in norbornene series. Thepolymer contained a structural unit expressed by the general formula(4′) at 50 mole % and another structural unit expressed by the generalformula (4′a) at 50 mole %. The structural units were expressed by thefollowing structural formulae.

The first structural unit was expressed by the general formula (4′)where R¹, R², R³, R⁴, R⁵ and R⁶ were hydrogen atoms, R⁷ and R⁸ werepropylene groups, i.e., [—(CH₂)₃—] bonded to each other for forming aring and n was 1. On the other hand, the second structural unit wasexpressed by the general formula (4′a) where R¹³ was hydrogen atom andR¹⁴ was t-butoxycarbonyl group.

The derivative of norbornene was synthesized as follows. 0.131 gram ofdi-μ-chlorobis [(η-allyl) palladium (II)] and 0.244 gram ofhexafluorosilver antimonate were dissolved in 22 milliliters ofchlorobenzene, and were agitated at room temperature. After 20 minutes,the reactant mixture was filtrated, and the filtrate was added tomixture containing 11.44 grams of the derivative of norbornene of thefourteenth example, 7.03 grams of 5-norbornene-2-carboxylic acid t-butylester, 0.1 milliliter of water and 85 milliliters of chlorobenzene. Thesolution was agitated for 20 hours at room temperature, and, thereafter,was added to 600 milliliters of methanol. Resin was precipitated, andwas filtrated. The resin was dissolved in 75 milliliters ofchlorobenzene, and 15 milliliters of methanol and 1.6 grams of sodiumborohydride were added thereto. Agitation was continued for 3 hours atroom temperature, and the solution was left as it was for 24 hours atroom temperature. Pd (0) particles were precipitated. The particles werefiltrated, and the filtrate was poured in 500 milliliters of methanol.Resin was precipitated, and was filtrated. Then, 8.86 grams of theobjective resin was obtained. The yield was 48%. The weight averagemolecular weight Mw was 13000, and the degree of dispersion Mw/Mn was2.36.

SEVENTEENTH EXAMPLE

The present inventors synthesized polymer in norbornene series whichcontained a structural unit expressed by the general formula (4′) at 25mole %, another structural unit expressed by the general formula (4′b)at 25 mole % and yet another structural unit expressed by the generalformula (4′c) at 50 mole %. The structural units were expressed asfollows.

The first structural unit was expressed by the general formula (4′)where R¹, R², R³, R⁴, R⁵ and R⁶were hydrogen atoms, R⁷ and R⁸ werepropylene groups, i.e., [—(CH₂)₃—] bonded to each other for forming aring and n was 1. On the other hand, the second structural unit wasexpressed by the general formula (4′b) where R¹⁵ was hydrogen atom andR¹⁶ was t-butoxycarbonyl group.

The polymer was synthesized as follows. 2 grams of the derivative ofnorbornene of the fourteenth example, 1.646 grams of3-tetracyclododecene-8-carboxylic acid t-butyl ester and 1.24 grams ofmaleic anhidride were dissolved in 10 milliliters of tetrahydrofuran ina 100 ml flask with a reflux tube. 41.5 milligrams of AIBN was added tothe solution, and was agitated in argon atmosphere at 60 degrees to 65degrees in centigrade. After 20 hours, the resultant solution wascooled, and the reactant mixture was poured into 100 milliliters ofether. The precipitate was filtrated, and was refined through theprecipitation, again. Then, 1.5 grams of polymer was obtained. The yieldwas 31%.

The polymer was analyzed. The weight average molecular weight Mw wasdetermined to be 5700 through GPC analysis, and the degree of dispersionMw/Mn was 2.34.

EVALUATIONS

The present inventors evaluated the polymer and chemically amplifiedresist as follows.

RESISTANCE AGAINST ETCHING

2 grams of the polymer of the fourth example was dissolved in 10 gramsof propyleneglycolmonoethylether acetate, and the solution was passedthrough a 0.2 micron Teflon filter. Subsequently, the filtrate was spunonto a 3-inch silicon wafer, and, thereafter, was baked on a hot plateat 90 degrees in centigrade for 60 seconds. A thin resist layer of 0.7micron thick was formed on the silicon wafer. The silicon wafer was putinto a chamber of a reactive ion etching system, which was manufacturedand sold by Nichiden-Anerba Corporation as DEM451. CF₄ gas was suppliedinto the chamber, and dry etching was carried out on the conditions thatthe electric power was 100 watts, pressure was 5 Pa and gas flow was 30sccm. After the dry etching, the resistance against the dry etching wasevaluated on the basis of the etching speed.

The resistance against the dry etching was evaluated for the polymer ofthe ninth example and the polymer of the sixteenth example as similar tothe polymer of the fourth example.

As comparative examples, novolak resist, poly (p-vinylphenol) and poly(methylmethacrylate) were evaluated as similar to the fourth, ninth andsixteenth examples. The poly (p-vinylphenol) was used as the basic resinfor KrF resist. The novolak resist and the poly (p-vinylphenol) weresold in the market. The poly (methylmethacrylate) did not have anybridged cyclic hydrocarbon group in the molecular structure. The valuesof the etching speed were normalized with respect to that of the novolakresist as shown in the following table.

Etching Speed Polymer (Relative Ratio) Example 4 1.2  Example 9 1.15Example 16 1.15 Poly (methylmethacrylate) 1.9  Poly (p-vinylphenol) 1.2 Novolak Resist (PFI-15A) 1  

The etching on the polymers according to the present invention wasslower than that on the poly (p-vinylphenol). Thus, the polymersaccording to the present invention exhibited large resistance againstthe dry etching.

TRANSPARENCY

1.8 grams of the polymer of the fourth example was dissolved in 10 gramsof propyleneglycolmonoethylether acetate, and the solution was filtratedthrough a 0.2 micron Teflon filter. Subsequently, the filtrate was spunonto a 3-inch quartz plate, and, thereafter, was baked on a hot plate at90 degrees in centigrade for 60 seconds. A thin resist layer of 0.4micron thick was formed on the quartz plate. Using anultra-violet/visual range spectrophotometer, the. present inventorsmeasured the transmittance to 193.4 nm wavelength ray, which was thecentral wavelength of ArF excimer laser light.

The transparency was also evaluated for the polymer in the acrylicseries, i.e., the ninth example and the polymer in the norborneneseries, i.e., the sixteenth example as similar to the polymer of thefourth example.

The transmittance of the fourth example was 83%/0.4 micron, thetransmittance of the ninth example was 81%/0.4 micron, and thetransmittance of the sixteenth example was 73%/0.4 micron. The presentinventors concluded that the polymers according to the present inventionexhibited transparency large enough to use it as a single layer resist.

PATTERN FORMING PROPERTY

The present inventors produced solution containing

(1) 2 grams of polymer in acrylic series obtained as the fourth example,

(2) 0.04 gram of triphenylsulfonium nonaflate serving as photo-acidgenerator, and

(3) 11.5 grams of propyleneglycolmonoethylether acetate.

The present inventors filtrated the solution with a 0.2 micron Teflonfilter, and produced a chemically amplified resist.

An 8-inch silicon wafer was coated with 0.1 micron organicanti-reflection layer, which was manufactured by Brewer Corporation asDUV-30J, and the chemically amplified resist was spun thereonto. Thechemically amplified resist was baked on a hot plate at 110 degrees incentigrade for one minute. Then, the anti-reflection layer was overlaidby a chemically amplified resist layer of 0.4 micron thick.

The silicon wafer coated with the chemically amplified resist layer wasput into an ArF reduction projection aligner, which was manufactured byNikon Corporation. The numerical aperture was 0.6. The chemicallyamplified resist layer was exposed to ArF excimer laser light so as toform a latent image therein.

After the exposure to the light, the silicon wafer was baked on the hotplate at 130 degrees in centigrade for 60 seconds, and, thereafter, wasdipped in 2.38% water solution of (CH₃)₄ NOH (TMAH) for 60 seconds. Thelatent image was developed. After the development, the chemicallyamplified resist layer was rinsed in pure water for 60 seconds, and apositive resist pattern was formed on the silicon wafer.

The present inventors similarly produced another sort of chemicallyamplified resist on the basis of the polymer in acrylic series producedas the ninth example and yet another sort of chemically amplified resistone the basis of the polymer in norbornene series produced as thesixteenth example. Using these sorts of chemically amplified resist, thepositive pattern was transferred to the chemically amplified resistlayers as similar to the above.

The present inventors evaluated those sorts of chemically amplifiedresist from the viewpoints of sensitivity and resolution. The evaluationwas summarized in the following table.

Chemically Amplified Resist Resolution Sensitivity Containing (μmL/S)(mJ/cm²⁾ Fourth example 0.14 20.4 Ninth example 0.13 15.6 Sixteenthexample 0.15 22.0

Thus, the present inventors concluded that the chemically amplifiedresist according to the present invention exhibited good pattern formingproperty.

ADHESION TO SUBSTRATES

The present inventors spread the chemically amplified resist accordingto the present invention on substrates, and observed the boundarybetween the chemically amplified resist layers and the substratesthrough a scanning electron microscopy. The chemically amplified resistlayers were strongly adhered to the substrates, and did not peel offThus, the present inventors concluded that the chemically amplifiedresist had good adhesion to substrates.

The present inventors evaluated other sorts of chemically amplifiedresist produced on the basis of other polymers in similar manners tothose described hereinbefore. The results were summarized as follows.

The present inventors confirmed that chemically amplified resistproduced on the basis of the polymer in acrylic series, i.e., each ofthe fifth to eighth and tenth to thirteenth examples exhibited largeresistance against etching, high transparency, high sensitivity, goodresolution and good adhesion to substrates.

The present inventors further confirmed that chemically amplified resistproduced on the basis of the polymer in norbornene series, i.e., theseventeenth example exhibited large resistance against etching, hightransparency, high sensitivity, good resolution and good adhesion tosubstrates. The present inventors further synthesized a derivative of(meth)acrylate expressed by the general formula (3) where n is zero. Aderivative of 3-oxo-4-oxabicyclo[3.2.1]otane reacted withtriphenylmethyllithium and, thereafter, with 1,2-dibromoethane to2-bromo compound. The 2-bromo compound reacted with (meth)acrylic acidin the presence of basic catalyst. Then, the present inventors obtained(meth)acrylate expressed by the general formula (3) where n is zero. Thederivative of (meth)acrylate reacted with cyclopentadiene. Then, aderivative of norbornene at n=zero was obtained. The monomers, i.e., thederivative of (meth)acrylate and the derivative of norbornene were vinylpolymerized to obtain polymer. Chemically amplified resist was producedon the basis of the polymer, and the present inventors evaluated thechemically amplified resist. The present inventors confirmed that thechemically amplified resist exhibited large resistance against etching,high transparency, high sensitivity, good resolution and good adhesionto substrates.

As will be appreciated from the foregoing description, the polymer andchemically amplified resist according to the present invention have thebridged alicylic δ lactone structure so that the large resistanceagainst dry etching, high transparency, good resolution and goodadhesion to substrates are achieve. Using the chemically amplifiedresist, the-manufacturer can transfer fine patterns to silicon wafers inthe fabrication process of ultra large scale integration in the nextgeneration

Although particular embodiments of the present invention have been shownand described, it will be apparent to those skilled in the art thatvarious changes and modifications may be made without departing from thespirit and scope of the present invention.

What is claimed is:
 1. A photoresist comprising polymer comprising vinylpolymer having 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl group expressed bygeneral formula (1)

where each of L¹, L², L³, L⁴, L⁵ and L⁶ is selected from the groupconsisting of hydrogen atom and alkyl groups having the carbon numberfrom 1 to 8, and photo-acid generator generating acid in the presence oflight equal in wavelength to or less than 220 nanometers, the ratio ofsaid photo-acid generator to said photoresist being fallen within therange from 0.2% by mass to 30% by mass.
 2. The photoresist as set forthin claim 1, in which one of said hydrogen atom and said alkyl groups atL⁵ and one of said hydrogen atom and said alkyl groups at said L⁶ arereplaced with alkylene groups having the carbon number from 1 to 10 andbonded to each other for forming a ring.
 3. The photoresist as set forthin claim 1, in which said vinyl polymer comprises at least onestructural unit polymerized with vinyl monomer selected from the groupconsisting of ethylene, derivatives of ethylene, vinyl chloride,derivatives of vinyl chloride, styrene, derivatives of styrene,acrylonitrile, derivatives of acrylonitrile, (meth)acrylate, derivativesof (meth)acrylate, norbornene carboxylic acid ester and derivatives ofnorbornene carboxylic acid ester.
 4. The polymer as set forth in claim3, in which the vinyl monomers in acrylic series have a bridged alicylicδ lactone structure expressed by general formula (3′)

where R¹ is selected from the group consisting of hydrogen atom andmethyl group, each of R² and R³ is selected from the group consisting ofhydrogen atom and alkyl groups having the carbon numbers from 1 to 4,each of R⁴, R⁵ and R⁶ is selected from the group consisting of hydrogenatom and methyl group, R⁷ and R⁸ are hydrogen atoms or alkylene groupshaving the carbon number from 1 to 10 and bonded to each other forforming a ring and n is zero or
 1. 5. The photoresist as set forth inclaim 3, in which the vinyl polymers in norbornene series have a bridgedalicylic δ lactone structure expressed by general formula (4′)

where R¹ is selected from the group consisting of hydrogen atom andmethyl group, each of R² and R³ is selected from the group consisting ofhydrogen atom and alkyl groups having the carbon number from 1 to 4,each of R⁴, R⁵ and R⁶ is selected from the group consisting of hydrogenatom and methyl group, R⁷ and R⁸ are hydrogen atoms or alkylene groupshaving the carbon number from 1 to 10 and bonded to each other forforming a ring and n is zero or
 1. 6. A photoresist comprising polymercomprising vinyl polymer having a bridged alicylic δ lactone structureexpressed by general formula (2)

where each of R² and R³ is selected from the group consisting ofhydrogen and alkyl groups having the carbon number from 1 to 4, each ofR⁴, R⁵ and R⁶ is selected from the group consisting of hydrogen atom andmethyl group, R⁷ and R⁸ are hydrogen atoms or alkylene groups eachhaving the carbon number from 1 to 10 and bonded for forming a ring andn is zero or 1, and photo-acid generator generating acid in the presenceof light equal in wavelength to or less than 220 nanometers, the ratioof said photo-acid generator to said photoresist being fallen within therange from 0.2% by mass to 30% by mass.
 7. The photoresist as set forthin claim 6, in which said vinyl polymer comprises at least onestructural unit polymerized with vinyl monomer selected from the groupconsisting of ethylene, derivatives of ethylene, vinyl chloride,derivatives of vinyl chloride, styrene, derivatives of styrene,acrylonitrile, derivatives of acrylonitrile, (meth)acrylate, derivativesof (meth)acrylate, norbornene carboxylic acid ester and derivatives ofnorbornene carboxylic acid ester.
 8. The photoresist as set forth inclaim 7, in which the vinyl polymers in acrylic series have a bridgedalicylic δ lactone structure expressed by general formula (3′)

where R¹ is selected from the group consisting of hydrogen atom andmethyl group, each of R² and R³ is selected from the group consisting ofhydrogen atom and alkyl groups having the carbon numbers from 1 to 4,each of R⁴, R⁵ and R⁶ is selected from the group consisting of hydrogenatom and methyl group, R⁷ and R⁸ are hydrogen atoms or alkylene groupshaving the carbon number from 1 to 10 and bonded to each other forforming a ring and n is zero or
 1. 9. The photoresist as set forth inclaim 7, in which the vinyl polymers in norbornene series have a bridgedalicylic δ lactone structure expressed by general formula (4′)

where R¹ is selected from the group consisting of hydrogen atom andmethyl group, each of R² and R³ is selected from the group consisting ofhydrogen atom and alkyl groups having the carbon number from 1 to 4,each of R⁴, R⁵ and R⁶ is selected from the group consisting of hydrogenatom and methyl group, R⁷ and R⁸ are hydrogen atoms or alkylene groupshaving the carbon number from 1 to 10 and bonded to each other forforming a ring and n is zero or 1.